In the commercial production of crops, it is desirable to easily and quickly eliminate unwanted plants (i.e., “weeds”) from a field of crop plants. An ideal treatment would be one which could be applied to an entire field but which would eliminate only the unwanted plants while leaving the crop plants unharmed. One such treatment system would involve the use of crop plants which are tolerant to a herbicide so that when the herbicide was sprayed on a field of herbicide-tolerant crop plants, the crop plants would continue to thrive while non-herbicide-tolerant weeds were killed or severely damaged. Ideally, such treatment systems would take advantage of varying herbicide properties so that weed control could provide the best possible combination of flexibility and economy. For example, individual herbicides have different longevities in the field, and some herbicides persist and are effective for a relatively long time after they are applied to a field while other herbicides are quickly broken down into other and/or non-active compounds. An ideal treatment system would allow the use of different herbicides so that growers could tailor the choice of herbicides for a particular situation.
Crop tolerance to specific herbicides can be conferred by engineering genes into crops which encode appropriate herbicide metabolizing enzymes and/or insensitive herbicide targets. In some cases these enzymes, and the nucleic acids that encode them, originate in a plant. In other cases, they are derived from other organisms, such as microbes. See, e.g., Padgette et al. (1996) “New weed control opportunities: Development of soybeans with a Roundup Ready® gene” and Vasil (1996) “Phosphinothricin-resistant crops,” both in Herbicide-Resistant Crops, ed. Duke (CRC Press, Boca Raton, Fla.) pp. 54-84 and pp. 85-91. Indeed, transgenic plants have been engineered to express a variety of herbicide tolerance genes from a variety of organisms.
While a number of herbicide-tolerant crop plants are presently commercially available, improvements in every aspect of crop production, weed control options, extension of residual weed control, and improvement in crop yield are continuously in demand. Particularly, due to local and regional variation in dominant weed species as well as preferred crop species, a continuing need exists for customized systems of crop protection and weed management which can be adapted to the needs of a particular region, geography, and/or locality. A continuing need therefore exists for compositions and methods of crop protection and weed management.